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Scientists are using magnetic resonance imaging to shed new light on how we make up our minds

As Scotland prepares to decide its future in the independence referendum, how will voters make up their minds? BBC Scotland's Science Correspondent Kenneth Macdonald asks whether the head or the heart will prove decisive.

Political scientists are increasingly adapting techniques from psychology and neurology to understand how we make political decisions.

Their findings suggest that our rational thought processes do play a part - but that our hearts are in the driving seat.

The science of campaigning will be examined on Tuesday in a BBC Scotland documentary.

Strictly speaking this is not really head vs heart, more the emotional circuits of our brain trumping the rational ones.

The slightly disturbing conclusion - disturbing, that is, for those of us who like to think they weigh up conflicting arguments with dispassionate, Spock-like logic - is that baser instincts are at play.

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The documentary tested an undecided volunteer for her responses to campaign messages

To examine the emotional underpinning of our political choices Dr Johns and I waylaid a self-selecting sample of BBC staff.

We were equipped with a ballot box and two photographs: one of a woman with a tarantula on her face, the other of a particularly nasty-looking verruca.

There were two questions on the ballot paper: Yes or No to independence, and a request to rate just how disgusting those photos were.

Given that our unsuspecting subjects had been waylaid on the way to lunch, this wasn't going to find its way into a peer reviewed journal. But the results were nonetheless intriguing.